Glossary of Terms
Impress your friends and loved ones at parties by knowing the difference between marquenching and ferritic carburizing
Impress your friends and loved ones at parties by knowing the difference between marquenching and ferritic carburizing
aging: A time temperature dependent change in the properties of certain alloy steels, as a change in properties that may occur gradually at atmospheric temperature (Natural ageing) and more rapidly at higher temperature (Artificial ageing).
age hardening: Hardening by aging, usually after rapid cooling or cold working
annealing: A generic term denoting a treatment, consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to: improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and/or increase in stability of dimensions. When the term is used without qualification, full annealing is implied. When applied only for the relief of stress, the process is properly called stress relieving or stress-relief annealing.
The time temperature cycle used vary widely both in maximum temperature attained and in cooling rate employed, depending on the composition of the steel, its condition, and the result desired. Various types of annealing processes are as follows:
austempering – It is quenching from a temperature above the transformation range to some temperature above the upper limit of martensite formation, and holding at this temperature until the austenite is completely transformed to the desired intermediate structure, for the purpose of conferring certain mechanical properties. It is carried out in a medium having a rate of heat abstraction high enough to prevent the formation of high temperature transformation products.
austenitizing – Forming austenite by heating into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.
blueing: A treatment of the surface of steels usually in the form of sheet or strip, on which, by the action of air or steam at a suitable temperature, a thin blue oxide film is formed on the initially scale free surface, as a means of improving appearance and resistance to corrosion. This term is also used to denote a heat treatment of springs after fabrication, to reduce the internal stress created by coiling and forming.
boronizing (bodding): A surface treatment procedure in which boron atoms are diffused into the work piece by thermochemical treatment for purpose of increased hardness, wear and corrosion resistance.
Brinell hardness test: A means of determining surface hardness by measuring the amount of resistance to the indentation of a steel ball. Recorded as the Brinell hardness number (BHN); the higher the number, the harder the material. Generally indicative of abrasion resistance.
carbonitriding: A case hardening process in which a suitable ferrous material is heated above the tower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workpiece.
carburizing: Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching.
case hardening: A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding; and carbonitriding. The use of the applicable specific process name is preferred.
cementation: The introduction of one or more elements into the outer portion of a metal object by means of diffusion at high temperature.
cooling curve: A curve showing the relation between time and temperature during the cooling of a material.
cryogenic treatment (cold treatment): Treatment carried out after quenching to transform retained austenite into martensite, involving cooling and holding at a temperature below ambient. It in essence squeezes a metal’s molecular structure, easing internal stresses that come from differences in grain density, improving dimensional stability and creating a denser microstructure.
decarburization: Loss of carbon from the surface layer of a carbon-containing alloy due to reaction with one or more chemical substances in a medium that contacts the surface.
dilatometer: An instrument for measuring the linear expansion or contraction in a metal resulting from changes in such factors as temperature and allotropy.
drawing: Drawing, or drawing the temper, is synonymous with Tempering, which is preferable.
embrittlement: The severe loss of ductility or toughness or both of a material, usually a metal or alloy. Many forms of embrittlement can lead to brittle fracture. Many forms can occur during thermal treatment or elevated-temperature service (thermally induced embrittlement).
eutectic: An isothermal reversible reaction in which a liquid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. (2) An alloy having the composition indicated by the eutectic point on an equilibrium diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectic reaction.
ferritic nitrocarburizing: A surface treatment process of ferrous metals involving diffusion of nitrogen and carbon into workpiece during ferritic phase, as opposed to austentic phase, for purpose of increased fatigue limit.
flame hardening: A process for hardening the surfaces of hardenable ferrous alloys in which an intense flame is used to heat the surface layers above the upper transformation temperature, whereupon the workpiece is immediately quenched.
gas nitriding: A case hardening process where nitrogen is added to surface of ferrous alloy at relatively low temperature. Need for quenching is eliminated.
heat treatment: Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.
heat treatment solution: A treatment in which an alloy is heated to a suitable temperature and held at this temperature for a sufficient length of time to allow a desired constituent to enter into solid solution, followed by rapid cooling to hold the constituent in solution. The material is then in a supersaturated, unstable state, and may subsequently exhibit Age Hardening
induction hardening: A surface-hardening process in which only the surface layer of a suitable ferrous workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched.
induction heating: Heating by combined electrical resistance and hysteresis losses induced by subjecting a metal to the varying magnetic field surrounding a coil carrying alternating current.
ion nitriding: A method of surface hardening in which nitrogen ions are diffused into a workpiece in a vacuum through the use of high-voltage electrical energy. Synonymous with plasma nitriding or glow-dischargenitriding.
ledeburite: The eutectic of the iron-carbon system, the constituents being austenite and cementite. The austenite decomposes into ferrite and cementite on cooling below the Ar1.
liquid nitrocarburizing: A nitrocarburizing process (where both carbon and nitrogen are absorbed into the surface) utilizing molten liquid salt baths below the lower critical temperature.
maraging: A precipitation hardening treatment applied to special steel to precipitate one or more of intermetallic compounds.
marquenching (martempering): (1) A hardening procedure in which an austenitized ferrous workpiece is quenched into an appropriate medium whose temperature is maintained substantially at the Ms of the workpiece, held in the medium until its temperature is uniform throughout—but not long enough to permit bainite to form— and then cooled in air. The treatment is frequently followed by tempering. (2) When the process is applied to carburized material, the controlling Ms temperature is that of the case. This variation of the process is frequently called marquenching.
martensite: A generic term for microstructures formed by diffusionless phase transformation in which the parent and product phases have a specific crystallographic relationship. Martensite is characterized by an acicular pattern in the microstructure in both ferrous and nonferrous alloys. In alloys where the solute atoms occupy interstitial positions in the martensite lattice (such as carbon in iron), the structure is hard and highly strained; but where the solute atoms occupy substitutional positions (such as nickel in iron), the martensite is soft and ductile. The amount of high-temperature phase that transforms to martensite on cooling depends to a large extent on the lowest temperature attained, there being a rather distinct beginning temperature (Ms) and a temperature at which the transformation is essentially complete (M1).
metallurgy: The science and technology of metals and alloys. Processmetallurgy is concerned with the extraction of metals from their ores and with refining of metals; physical metallurgy, with the physical and mechanical properties of metals as affected by composition, processing, and environmental conditions; and mechanical metallurgy, with the response of metals to applied forces.
nitriding: Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.
nitrocarburizing: Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create aconcentration gradient. Nitrocarburizing is done mainly toprovide an antiscuffing surface layer and to improvefatigue resistance. Compare with carbonitriding. : Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.
quenching: Hardening of carbon steel in an oil bath. Oils are categorized as conventional, fast, martempering, or hot quenching.
pearlite: A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range.
phase diagram: A graphical representation of the temperature and composition limits of phase fields in an alloy system as they actually exist under the specific conditions of heating or cooling (synonymous with constitution diagram). A phase diagram may be an equilibrium diagram, an approximation to an equilibrium diagram, or a representation of metastable conditions or phases.
precipitation hardening: Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening.
press quenching: A quench In which hot dies are pressed and aligned with a part before the quenching process begins. Then the part is placed in contact with a quenching medium in a controlled manner. This process avoids part distortion.
pyrometer: A device for measuring temperatures above range of liquid thermometers.
quenching: Rapid cooling. When applicable, the following more specific terms should be used: Direct Quenching, Fog Quenching, Hot Quenching, Interrupted Quenching, Selective Quenching, Slack Quenching, Spray Quenching, and Time Quenching.
Rockwell hardness test: An indentation hardness test based on the depth of penetration of a specified penetrator into the specimen under certain arbitrarily fixed conditions.
salt bath heat treatment: Heat treatment carried out in a bath of molten salt.
shot blasting (shot blast cleaning): Uses steel shot to remove scale from heat treated parts. This cleaning process provides a finished product with a bright metallic shine. Typically forgings and castings are subjected to this type of cleaning, which is considerably more aggressive than glass beading.
spalling: A chipping or flaking of a surface due to any kind of improper heat treatment or material dissociation.
straightening: A process by which a long, slender metal part is straightened to a specified tolerance, typically following hardening of the material. This can be a cold mechanical process performed on a straightening press or it can involve the use of heat in a fixture or die.
stress relieving: Heating to a suitable temperature, holding long enough to reduce residual stresses, and thencooling slowly enough to minimize the development of new residual stresses.
superficial hardness test: A test to determine surface hardness of thin sheet material which applies relatively light loads producing minimal penetration and damage.
tempering: Heating a quench hardened or normalized ferrous alloy to a temperature below the transformation range to produce desired changes in properties. The object of tempering or drawing is to reduce the brittleness in hardened steel and to remove the internal strains caused by the sudden cooling in the quenching bath. The tempering process consists in heating the steel by various means to a certain temperature and then cooling it. When steel is in a fully hardened condition, its structure consists largely of martensite. On reheating to a temperature of from about 300 to 750°F., a softer and tougher structure known as troostite is formed. If the steel is reheated to a temperature of from 750 to 1290°F, a structure known as a sorbite is formed, which has somewhat less strength than troostite, but much greater ductility.
vacuum furnace: A furnace using low atmospheric pressures instead of a protective gas atmosphere like most heat-treating furnaces. Vacuum furnaces are categorized as hot wall or cold wall, depending on the location of the heating and insulating components.
vacuum heat treating: The process, at a temperature up to 1000°C and higher, in which metallic/steel parts are exposed completely or partially to time-temperature sequences in order to change the mechanical and/or corrosion properties. Application areas include Annealing, Hardening, Tempering, Aging and Case hardening to achieve a higher strength of the material, better wear resistance or to improve the corrosion behavior of the components.